1. Technical Field
The inventions disclosed in this application relate to methods for winding an automotive tire building strip member on a building drum.
More particularly, the first invention in this application provides a method for winding a strip member such as rubberized steel cord, tread rubber or the like precut to the circumferential length of the building drum of a tire building machine, on said building drum in such a manner that both ends of the strip member will be exactly abutted against each other on the drum.
The second invention in this application relates to an automotive tire building device wherein the lapping margin of ends of a strip member wound on its building drum can be automatically measured.
2. Prior Art
In winding a tire strip member on a building drum, it is at times required to insure exact abutment of its ends and at other times required that the lapping margin (positive and negative) be within certain allowable limits.
As a technology for insuring exact abutment of both ends of a strip member such as rubberized steel cord or tread rubber in the winding thereof on the building drum of an automotive or other tire building machine, there is known the method described in Japanese Patent Publication No. 61-32980. According to this method, the length of the strip precut to the circumferential length of the building drum is measured and, then, a leading portion, of predetermined length, of the strip is taken up on the building drum at the feeding (takeup) speed equal to the peripheral speed of the drum. Then, the feeding speed relative to the building drum speed is altered to either compress or stretch the strip while its intermediate portion is wound on the building drum. Finally, the feeding speed is re-equalized with the peripheral speed of the building drum to wind up the remaining portion of the strip member on the drum.
However, the strip member tends to shrink with the progress of time after cutting and the time to termination of shrinkage and the amount of shrinkage are dependent on the environment and other conditions. Under certain conditions, the amount of post-cutting shrinkage reaches as much as about 0.5%. Moreover, the length of the strip member varies with the magnitude of the tension that acts on the strip when it is transferred from a transfer conveyer to the building drum and the pressure of contact between the strip and the drum. In the prior art method mentioned above, the total length of the strip member is measured while it is undergoing shrinkage after cutting and the ratio of the feeding speed to the peripheral speed of the building drum is set according to the length value thus found so as to compress or stretch the intermediate portion of the strip. As a consequence, the aforesaid ratio is often irrelevant and there occurs an excess or a shortage of compression or stretching of the strip member, thus causing a lapping of the leading and trailing ends of the strip member or a gap therebetween.
Therefore, the first invention in this application provides a winding method which insures exact abutment of said ends or abutment without an appreciable overlap or gap.
Furthermore, in the process of manufacture of an automotive tire, not only the steel cord and tread rubber mentioned above but a variety of other rubber-based strip members are cut to length and both ends thereof are joined to build single-layer or multi-layer ring or cylindrical members. For example, on the primary building machine, an inner liner (a strip member of rubber) and a plurality of ply cords (rubberized fiber cords or steel cords), all precut to the circumferential length of the building drum, are laid up on the peripheral surface of the drum. In the secondary building machine, two steel belts (rubberized steel cords), a cap ply (rubberized nylon cord), etc. are laid up. Some of these different strip members are not joined by abutment at ends as described above but are joined by lapping the trailing end over the leading end on the drum. As mentioned above, the strip member has the property to shrink on standing after cutting to length as mentioned above and the amount of this shrinkage varies with changes in environment. Also as mentioned above, the length of the strip member is altered by external forces that act on the strip when it is transferred from the conveyer to the drum. Therefore, even if the strip member has been cut precisely to length, a variation is inevitable in the degree of lapping of both ends. Therefore, it is common practice for the operator to trim off the rubber or cord at the trailing end when the degree of lapping is too large or unwind the strip partway and rewind it with stretching when there is a gap between ends.
However, the conventional tire building machine is not equipped with very effective means for inspecting the end joint of said strip member and the current trend toward automation of tire building cannot completely avoid a risk of products with said surplus or deficiency in end lapping being shipped uncorrected and marketed.
Accordingly the second invention in this application provides a tire building device which is capable of detecting a surplus or deficiency in end lapping while a strip member is wound on a building drum of said primary or second building machine.
The method for winding a strip member on a tire building machine in accordance with the first invention in this application comprises feeding a strip member to a building drum by means of a transfer conveyer, taking up said strip member on said building drum while controlling the speeds of said transfer conveyer and building drum and joining free ends of the strip member, which method is characterized by setting the feeding speed of said transfer conveyer and the peripheral speed of said building drum to equal values, taking up a leading portion, of predetermined length, of said strip member on the building drum, detecting the position of a trailing end of said strip member on said transfer conveyer to calculate the length of a trailing portion following said leading portion of said strip member, setting the ratio of the feeding speed of said transfer conveyer to the peripheral speed of said building drum to the ratio L/Lo, where L is the length of said trailing portion and Lo is the residual circumferential length of said building drum, only when the L/Lo ratio is within a set range and taking up the trailing portion of said strip member, while the takeup of the trailing portion of said strip member is stopped when the ratio L/Lo deviates out of said set range.
Thus, after completion of the takeup of a leading portion of the strip member or just before the beginning of takeup of a trailing portion of the strip member, the length of the trailing portion is measured and the trailing portion is wound only when the ratio L/Lo of the length of the trailing portion of the strip member to the residual circumferential length Lo of the building drum is within a set range, with the ratio of the feeding speed to the peripheral speed of the building drum being set to said ratio L/Lo, with the result that the error of length L of the trailing portion of the strip member is minimized to preclude an excessive overlap or gap between ends of the strip member, thus leading to exact abutment of the ends or a minimum of overlap or gap.
The length of the leading portion of said strip member is preferably set to 30xcx9c80% of one circumferential length of the building drum. If the set length is less than 30%, installation of a leading end sensor is difficult. Conversely if the set length is over 80%, the stretching or compression of the strip member is concentrated in the trailing portion thereof to adversely affect the quality of the product.
The said ratio L/Lo applicable to the case of continued takeup of the trailing portion of the strip member is preferably set within the range of 0.9995xcx9c1.005. Outside of this range, the amount of stretching or compression becomes too great to insure the proper winding.
The method of winding the strip member in accordance with the second invention in this application comprises using a tire building machine having a building drum for taking up a tire-building strip member of predetermined length endlessly and a transfer conveyer for feeding said strip member to said building drum, which method is characterized by detecting the winding-start end of said strip member transferred from said transfer conveyer to said building drum and the winding-finish end of said strip member with end sensors, measuring the angle through which said building drum has rotated from the output of a winding start signal to the output of a winding finish signal in response to output signals from said sensors by means of an angle detector, and calculate a lapping margin between the winding start end and the winding finish end of said strip member based on the rotational angle and diameter of said building drum by means of an operational meals.
In the above method, since the lapping margin between the two ends of the strip member is calculated by said operational means, the building operation can be continued while said lapping margin is within a preset allowable range or the operation can be discontinued or an alarm be actuated when the lapping margin deviates out of said allowable range, that is to say when the lapping margin is too large or too samll. Therefore, in the automatic building process for car tires, the risk of products with lapping defects being shipped can be effectively prevented.
It may be so arranged that one end sensor of the above-described type is used to detect both the winding start and winding finish ends of the strip member or that two such end sensors are installed apart from each other by an optional angle along the circumferential direction of the building drum so that one of the sensors is used to detect the winding start end with the other sensor deteting the winding finish end.
Furthermore, a still more improved accuracy may be insured by installing end sensors in a plurality of positions, for example in the center and in positions on both sides thereof. Moreover, to cope with the case in which one strip member has an intermediate joint of material and this joint builds a step, it may be so arranged that the trailing end sensor is rendered operative only within a certain range, for example in the range of 5 mm, before and after the winding start end, whereby the risk of said joint being mistaken for the winding finish end and detected as such.
In the second invention in this application, the lapping margin of the strip member wound on the building drum includes both a positive value and a negative value. In other words, the case in which the two ends of the strip member actually overlap and the case in which there is a gap between the ends are included. The winding operation is stopped when the actual overlap or gap is too great or too small.